The Merksplas-Beerse geothermal well (17W265) and the Dinantian reservoir
Abstract
The Merksplas-Beerse well (North Belgium) is a low-enthalpy geothermal production well targeting the Dinantian karstic limestones to a total depth of 1761 m. The presence of methane gas in these limestones generated a particular interest in this well. This paper describes the geological profile of this well and the Dinantian reservoir. The Namurian-Visean boundary at 1630 m is determined by the base of the dipmeter draping pattern in the radioactive Chokier shales (base of the Namurian) on top of the karstified Dinantian limestone. The stratigraphic composition of the transitional interval from Dinantian to Silesian correlates closely to the nearby Turnhout well. The two fractured intervals at 1630-1656 and 1739-1747 m respectively were identified in the Dinantian limestones. They are associated with siliciclastic sections in between pure limestones.
The reservoir water is a sodium chloride brine of about 74 °C and at a pressure below the hydrostatic. The water is slightly radioactive because of the contact with the Chokier hot shales. A carbon dioxide gas with methane and nitrogen admixture is dissolved in the water. The gas liquid ratio at standard conditions is about one and the bubble point is around 200-400 psi at reservoir temperature. A long duration pumping test shows a high fracture permeability and a productivity index of 5.4 m3/h/bar with a productivity to injectivity ratio of 1.45.